NEW ROCKET TECHNOLOGY COULD CUT MARS TRAVEL TIME

An agreement to collaborate on development of an advanced
rocket technology that could cut in half the time required to
reach Mars, opening the solar system to human exploration in the
next decade, has been signed by NASA's Johnson Space Center,
Houston, TX, and MSE Technology Applications Inc., Butte, MT.

The technology could reduce astronauts' total exposure to
space radiation and lessen time spent in weightlessness, perhaps
minimizing bone and muscle mass loss and circulatory changes.

Called the Variable Specific Impulse Magnetoplasma Rocket
(VASIMR), the technology has been under development at Johnson's
Advanced Space Propulsion Laboratory. The laboratory director is
Franklin Chang-Diaz, a NASA astronaut who holds a doctorate in
applied plasma physics and fusion technology from the
Massachusetts Institute of Technology, Cambridge.

Chang-Diaz, who began working on the plasma rocket in 1979,
said, "A precursor to fusion rockets, the VASIMR provides a power-
rich, fast-propulsion architecture."

Plasma, sometimes called the fourth state of matter, is an
ionized (or electrically charged) gas made up of atoms stripped of
some of their electrons. Stars are made of plasma. It is gas
heated to extreme temperatures, millions of degrees. No known
material could withstand these temperatures. Fortunately, plasma
is a good electrical conductor. This property allows it to be
held, guided and accelerated by properly designed magnetic fields.

The VASIMR engine consists of three linked magnetic cells.
The forward cell handles the main injection of propellant gas and
its ionization. The central cell acts as an amplifier to further
heat the plasma. The aft cell is a magnetic nozzle, which
converts the energy of the fluid into directed flow.

Neutral gas, typically hydrogen, is injected at the forward
cell and ionized. The resulting plasma is electromagnetically
energized in the central cell by ion cyclotron resonance heating.
In this process radio waves give their energy to the plasma,
heating it in a manner similar to the way a microwave oven works.

After heating, the plasma is magnetically exhausted at the
aft cell to provide modulated thrust. The aft cell is a magnetic
nozzle, which converts the energy of the plasma into velocity of
the jet exhaust, while protecting any nearby structure and
ensuring efficient plasma detachment from the magnetic field.

A key to the technology is the capability to vary, or
modulate, the plasma exhaust to maintain optimal propulsive
efficiency. This feature is like an automobile's transmission
which best uses the power of the engine, either for speed when
driving on a level highway, or for torque over hilly terrain.

On a mission to Mars, such a rocket would continuously
accelerate through the first half of its voyage, then reverse its
attitude and slow down during the second half. The flight could
take slightly over three months. A conventional chemical mission
would take seven to eight months and involve long periods of
unpowered drift en route.

There are also potential applications for the technology in
the commercial sector. A variable-exhaust plasma rocket would
provide an important operational flexibility in the positioning of
satellites in Earth orbit.

Several new technologies are being developed for the concept,
Chang-Diaz said. They include magnets that are super-conducting
at space temperatures, compact power generation equipment, and
compact and robust radio-frequency systems for plasma generation
and heating.

Coordinated by Johnson's Office of Technology Transfer and
Commercialization, the Space Act Agreement calls for a joint
collaborative effort to develop advanced propulsion technologies,
with no money exchanged between the two parties. Such agreements
are part of NASA's continuing effort to transfer benefits of
public research and development to the private sector.